1. Field of the Invention
This invention relates to a washing machine, more particularly, a washing machine having a dual damping structure, which can effectively prevent undesirable vibration by lowering the center of gravity of an outer tub depending on a quantity of washing objects and washing liquid in order to stabilize the outer tub.
2. Prior Art
Generally, washing machines are classified into a fully-automatic washing machine and a semi-automatic washing machine according to the operating manner.
As is well known, the fully-automatic washing machine carries out washing, rinsing, and dehydrating operations with washing objects in a single spin tub, so that there is no need to provide a separate dehydration tub for extracting washing liquid from the washed washing objects. On the contrary, the semi-automatic washing machine has a washing tub and a separate dehydration tub to carry out the washing and dehydrating operations, respectively.
Recently, the fully-automatic washing machines are widely being used as a household washing machine.
However, since the spin tub having relatively large volume is rotated at a high speed, the fully-automatic washing machine generates a vibration during the washing and dehydrating operations.
In particular, when the washing objects are unevenly distributed within the spin tub, an extreme vibration may be created so that not only a loud noise is generated, but also in an extreme case the washing machine moves from its initial position.
To overcome the above-mentioned problems, there has been effort to provide a fully-automatic washing machine which can prevent undesirable vibration thereof.
FIG. 1 shows such a conventional fully-automatic washing machine 300 having an assembly 330 for damping vibration.
As shown in FIG. 1, the conventional full-automatic washing machine comprises a body 305 having a plurality of projecting parts 307 formed in an upper portion of its inner wall, an outer tub 310 having a plurality of protuberances 312 formed in a lower portion of its outer wall, a spin tub 320 mounted in the outer tub 310 so as to receive washing objects, a motor 340 for rotating the spin tub 320, and a plurality of assemblies 330 for damping vibration caused by rotation of the spin tub 320.
Each of the projecting parts 307 and protuberances 312 has a hole (not shown) for fitting the vibration damping assembly 330.
The vibration damping assembly 330 includes a supporting member 332 fitted to the hole of projecting part 307 and formed with a perforated hole at a center thereof, a rod 334, one end of which is inserted in the perforated hole and the other end of which is fitted to the hole of protuberances 312, a cap 336 having an open end and disposed at an underside of protuberances 312 in order to dampen vibration of outer tub 310, and a stopper 339 inserted into the open end of the cap 336.
The conventional fully-automatic washing machine 300 has four vibration damping assemblies 300.
The operation of the conventional fully-automatic washing machine 300 being constructed as described above is as follows.
Firstly, in the event of a washing operation, when a user pushes an operating button (not shown) disposed in an upper portion of washing machine 300 on, a control unit such as micro-computer generates a signal for washing operation, and thereby the motor 340 is driven. The driving force of the motor 340 is transmitted to a pulsator 322 disposed in a lower portion of the spin tub 320 so that the pulsator 322 is rotated. As the pulsator 322 rotates, a liquid flow having a swirl shape is generated in the spin tub 320. The liquid flow that has been generated in the spin tub 320 impacts on washing objects, which have been loaded in the spin tub 320, and thereby the washing objects are washed.
Then, when the washing operation has finished, the washing liquid that has been supplied to the outer tub 310 is drained into an exterior of washing machine 300. In this state, the control unit generates a signal for a dehydrating operation, and thereby the motor 340 is driven again. At this time, the driving force of the motor 340 is transmitted to the spin tub 320 so that the spin tub 320 is rotated.
As the spin tub 320 rotates, the washing objects loaded in the spin tub 320 are subjected to centrifugal force so that the washing objects are forced radially outward of the spin tub 320, i.e., toward a side wall of the spin tub 320, and thereby the washing liquid contained in the washed washing objects is drained into an exterior of the washing machine 300 through a plurality of openings formed in the side wall of the spin tub 320.
During the washing and dehydrating operations, vibration inevitably happens in the washing machine 300. In particular, the vibration may occur more extremely during the dehydrating operation since the spin tub 320 having a relatively large size is rotated at a high speed.
To reduce the vibration, the conventional washing machine 300 comprises a plurality of vibration damping assemblies 330. The vibration damping assemblies 330 are regularly disposed around a circumference of the outer tub 310 so as to effectively dampen the vibration caused by high-speed rotation of the spin tub 320.
That is, the vibration that has been generated by rotation of the spin tub 320 or pulsator 322 is transmitted to the cap 336 of the vibration damping assembly 330, which is in contact with the protuberance 312 of the outer tub 310, through the outer tub 310. At this time, the spring 338 disposed in the cap 336 is repeatedly compressed and expanded according to the vibration so that the vibration can be dampened. The dampened vibration is transmitted to the support member 332 through the rod 334 connected to the cap 336 so that only a reduced vibration is transmitted to the body 305 of the washing machine 300.
However, the conventional automatic washing machine 300 being constructed as described above has the following disadvantages.
Firstly, because a supporting point of the vibration damping assembly 330 relative to the outer tub 310 is always fixed at a consistent position, in case of loading a large quantity of washing objects, the center of gravity of the outer tub 310 is placed at an upper portion as compared with the initial state. Therefore, the outer tub 310 is unstably supported, and thus the vibration of the outer tub 310 may not be effectively absorbed.
Further, when the washing objects are unevenly distributed within the spin tub 320, a relatively heavier vibration is transmitted to an upper portion of the body 305 of the washing machine 300 so that a loud noise may happen.
Accordingly, there has been a necessity to provide a washing machine having a dual damping structure which can effectively prevent the vibration.